Process for supplying oxygen and/or nitrogen and also argon to a geographic zone

ABSTRACT

In a process for supplying oxygen and/or nitrogen and also argon to a geographic zone, the geographic zone comprising n units for air separation by cryogenic distillation, of which a first unit and n-1 second units produce oxygen and/or nitrogen but do not produce argon, the oxygen and/or nitrogen for at least certain clients come from at least one of the n-1 second, non-argon-producing units, and argon for these clients comes from the first unit, where the first unit operates by means of a column system comprising a double column composed of a higher pressure column operating at a first pressure and a lower pressure column, whose bottom is connected thermally to the top of the higher pressure column, operating at a second pressure, which is lower than the first pressure, and of an argon-producing column and a mixing column, wherein the mixing column is fed at the bottom with an auxiliary gas consisting of gaseous nitrogen from the first or the lower pressure column, and at the top with a liquid which is richer in oxygen than the auxiliary gas and is taken from the lower part of the low-pressure column, and impure oxygen constituting a production gas is withdrawn at the top of the mixing column, the argon-producing column is fed with an argon-enriched gas flow from the lower pressure column, and an argon-rich product is withdrawn from the argon-producing column.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119 (a) and (h) to French patent application No. FR2005088, filed May 19, 2020, the entire contents of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a process for supplying oxygen and/or nitrogen and also argon to a geographic zone using cryogenic air distillation units.

BACKGROUND OF THE INVENTION

The rise in the proportion of renewable and intermittent energy sources (solar, wind, etc.) adds value to the capacity to curtail the electricity consumption of energy-intensive installations such as air separation units (ASUs).

Unfortunately, when these units produce argon, their dynamic characteristics make curtailing them relatively ineffective, since return to the nominal conditions of the main argon-producing column takes a good deal of time.

There are solutions available for reducing this time (EP3604994).

There are also methods enabling a significant portion of the nominal energy to be curtailed without changing the operating regime of the distillation columns.

SUMMARY OF THE INVENTION

The subject of the invention is a different route: in a region within which it is economical to transport liquid argon (with a radius typically of 1000 km) and where a number (n) of distributed air-distillation air separation units are needed to supply the market with oxygen and with nitrogen, a first, argon-producing unit and n-1 second, non-argon-producing, air-distillation air separation units are installed.

The post-halt steady-state return time of these n-1 second units is preferably less than 4 h (preferably less than 2 h).

Argon is also easy to transport over long distances, which is not the case for oxygen and nitrogen.

A first air-distillation air separation unit processes a flow of air sufficient to cover the entire argon demand of the zone, this flow being preferably in great excess relative to the oxygen and nitrogen demand of the site where the unit is located. The oxygen and nitrogen which are separated but not sold are remixed by a system featuring at least one mixing column, the aim being to recover part of the corresponding energy in the form of liquefied or compressed products.

The air flow processed by this unit is substantially constant irrespective of the energy availability conditions, whereas the n-1 second units are halted when the energy availability conditions make it desirable or necessary to do so.

The combination of such an assembly with one or more ASUs corresponding to the solutions described in the introduction is also claimed.

The combination of these solutions with other ASUs of any type, preexisting or yet to be constructed, shall also be protected.

It is known practice for air to be separated using a mixing column fed at the bottom with gaseous nitrogen and at the top with liquid oxygen, from WO8700609, for example. The two phases, liquid and gaseous, undergo mixing in the column—hence the name—and generate heat in the process. A technical class, F25J3/0446, is dedicated to such systems in the Cooperative Patent Classification.

According to one subject of the invention, a process is provided for supplying oxygen and/or nitrogen and also argon to a geographic zone, the geographic zone comprising n units for air separation by cryogenic distillation, of which a first unit and n-1 second units produce oxygen and/or nitrogen but do not produce argon, wherein the oxygen and/or nitrogen for at least certain clients in the geographic zone come from at least 1 of the n-1 second, non-argon-producing units, and argon for these clients comes from the first unit, where the first unit operates by means of a column system comprising a double column composed of a first column operating at a first pressure and a second column, whose bottom is connected thermally to the top of the first column, operating at a second pressure, which is lower than the first pressure, and of an argon-producing column and a mixing column, wherein the mixing column is fed at the bottom with an auxiliary gas consisting of gaseous nitrogen from the first or the second column, and at the top with a liquid which is richer in oxygen than the auxiliary gas and is taken from the lower part of the second column, and impure oxygen constituting a production gas is withdrawn at the top of the mixing column, the argon-producing column is fed with an argon-enriched gas flow from the second column, and an argon-rich product is withdrawn from the argon-producing column.

According to other subjects of the invention:

-   -   the argon for at least these at least certain clients comes         solely from the first unit.     -   at least some of the n-1 second units are halted if the price of         electricity increases beyond a threshold.     -   the first unit is not halted if the price of electricity         increases beyond the threshold.     -   the post-halt steady-state return time for one or even each of         the n-1 second units is less than that for the first unit.     -   the first unit does not supply the clients that it supplies with         argon with oxygen.     -   the first unit supplies all of the clients in a zone with argon         and/or constitutes the only unit supplying the clients in a zone         with argon.     -   the first unit receives a flow of air for separation which is         greater than that needed to produce a flow of oxygen that it         produces as an end product.     -   the assembly of units is located outside the geographic zone.     -   at least one unit of the assembly is located in the geographic         zone.

According to another subject of the invention, an assembly of units for air separation by cryogenic distillation for supplying oxygen and/or nitrogen and also argon to a geographic zone is provided, the assembly comprising n units for air separation by cryogenic distillation, of which a first unit and n-1 second units produce oxygen and/or nitrogen but do not produce argon, means for transporting the oxygen and/or nitrogen for at least certain clients in the geographic zone from at least 1 of the n-1 second, non-argon-producing units, and means for transporting argon for these clients from the first unit, where the first unit operates by means of a column system comprising a double column composed of a first column operating at a first pressure and a second column, whose bottom is connected thermally to the top of the first column, operating at a second pressure, which is lower than the first pressure, and of an argon-producing column and a mixing column (6), means for feeding the mixing column at the bottom with an auxiliary gas consisting of gaseous nitrogen from the first or the second column, and means for feeding the mixing column at the top with a liquid which is richer in oxygen than the auxiliary gas and is taken from the lower part of the low-pressure column, and means for withdrawing impure oxygen constituting a production gas at the top of the mixing column, means for feeding the argon-producing column with an argon-enriched gas flow from the second column, and means for withdrawing an argon-rich product from the argon-producing column.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparent from the description hereinafter of embodiments, which are given by way of illustration but without any limitation, the description being given in relation with the following attached figures:

FIG. 1 represents schematically one embodiment of an air distillation process used in a process according to the invention,

FIG. 2 represents schematically one embodiment of the argon and oxygen supply process according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 represents schematically an air distillation process intended for producing, for example, impure oxygen, having a purity for example of 80% to 97% and preferably of 85 to 95 percent, and also argon in a first unit used in the process according to the invention.

The installation comprises essentially a heat exchange line 1, a double distillation column 2 in turn comprising a first, medium-pressure column 3 operating at a first pressure, a low-pressure column 4 operating at a second pressure, which is lower than the first pressure, and a main vaporizer-condenser. It further comprises a mixing column 6. Columns 3 and 4 typically function at approximately 6×10 Pa and approximately 1×10 Pa, respectively. The operating pressure of the mixing column may be below, above or the same as the second pressure.

As explained in detail in document U.S. Pat. No. 4,022,030, a mixing column is a column which has the same structure as a distillation column but which is used for mixing, in a manner close to reversibility, a relatively volatile gas introduced at the column base and a less volatile liquid introduced at the column top.

Such mixing produces frigorific energy and so reduces the energy consumption linked to the distillation. In the present case this mixing is utilized additionally for direct production of impure oxygen at the pressure P and also of argon as will be described below.

The air for separation by distillation, compressed to 6×10 Pa and suitably purified, is conveyed to the base of the medium-pressure column 3 by a pipe 7. The major part of this air is cooled in the exchange line 1 and introduced at the base of the medium-pressure column 3, and the rest, boost-compressed in 8 then cooled, is expanded to the low pressure in a turbine 9 coupled to the booster compressor 8, then injected at an intermediate point of the low-pressure column 4. “Rich liquid” (oxygen-enriched air), taken from the bottom of the column 3, is expanded in an expansion valve 10 and then introduced into the column 4, at about the air injection point. “Poor liquid” (impure nitrogen), taken from an intermediate point 11 of the column 3, is expanded in an expansion valve 12 and then introduced at the top of the column 4, constituting the residual gas of the installation, and the pure gaseous nitrogen at the medium pressure, produced at the top of the column 3, are reheated in the exchange line 1 and discharged from the installation. These gases are indicated respectively by NI and NG in FIG. 1.

Liquid oxygen, of greater or lesser purity according to the regulation of the double column 2, is withdrawn from the bottom of the column 4, brought by a pump 13 to a pressure P1, which is slightly higher than the aforesaid pressure P to take account of head losses (P1-P less than 1×10 Pa), and introduced at the top of the column 6. In this example, then, P1 is advantageously the same as the first pressure. Gaseous nitrogen 13 at the same pressure P1, cooled in the subcooler 21, is introduced at the base of the mixing column 6. Withdrawn from this column are three fluid streams: at its base, liquid close to the rich liquid and combined therewith via a pipe 15 fitted with an expansion valve 15A; at an intermediate point, a mixture consisting essentially of oxygen and nitrogen, which is sent to an intermediate point of the low-pressure column 4 via a pipe 16 fitted with an expansion valve 17; and, at its top, impure oxygen, which is reheated in the heat exchange line and then discharged, substantially at the pressure P, from the installation via a pipe 18 as a production gas 0I.

Also shown in FIG. 1 are auxiliary heat exchangers 19, 20, 21 for recovering the cold available in the fluids circulating in the installation.

The installation further comprises a column 25 for producing impure argon, which is coupled, conventionally, to the low-pressure column 4.

The invention therefore enables the simultaneous production, under particularly economical conditions in terms of capital investment and energy consumption, of pure or nearly pure oxygen, impure oxygen and argon.

FIG. 2 shows a process according to the invention for supplying oxygen and argon to a zone comprising two clients C1, C2.

The figure illustrates the invention for n air separation units ASU1, ASU2, ASU3, n thus being 3.

Units ASU1, ASU2, ASU3 are units for air separation by cryogenic distillation which may be inside the zone or outside the zone.

Unit ASU1 is a first unit, and units ASU2 and ASU3 are second units.

Unit ASU2 and unit ASU3 do not produce argon and preferably do not include an argon-producing column or mixing column. They may both consist of a double column composed of a first column operating at a first pressure and a second column, whose bottom is connected thermally to the top of the first column, operating at a second pressure, which is lower than the first pressure.

Each of units ASU2 and ASU3 sends liquid oxygen to each of the two clients C1, C2 in the pentagonal zone Z. They do not send argon to these two clients.

The two clients C1, C2 are delivered liquid argon from the first unit ASU1. The first unit ASU1 functions according to the process illustrated in [FIG. 1] and comprises a double column composed of a first column operating at a first pressure and a second column, whose bottom is connected thermally to the top of the first column, operating at a second pressure, which is lower than the first pressure, and of an argon-producing column and a mixing column 6.

The unit ASU1 produces oxygen for a client C, but the magnitude of the columns and the air flow is for much greater production than is required for the client C. Additional liquid oxygen and gaseous nitrogen are fed to the mixing column in order to produce frigories. The argon column produces liquid argon, which is delivered to the clients C1, C2 and optionally to the client C on the site of ASU1.

If the price of electricity becomes excessive, and increases beyond a given threshold, units ASU2, ASU3 are halted, but unit ASU1 continues to function. The air flow processed by this unit ASU1 is substantially constant irrespective of the energy availability conditions, whereas the other two units ASU2, ASU3 are halted when the energy availability conditions make it desirable or necessary to do so.

The post-halt steady-state return time of these n-1 second units ASU2, ASU3 is preferably less than 4 h (preferably less than 2 h) for each. Thus the majority of the units do not produce argon and are therefore able to return to the steady state relatively quickly.

The number of units producing argon, and therefore having a steady-state return time of more than 2 h, probably more than 4 h, is reduced to just one.

The first unit ASU1 can produce argon for clients other than C1 and C2.

As used herein, means for sending/transferring/transporting/feeding/etc. . . . a fluid is understood to include one or more conduits and the like that are configured to transfer fluids from one location to another location.

While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications, and variations as fall within the spirit and broad scope of the appended claims. The present invention may suitably comprise, consist or consist essentially of the elements disclosed and may be practiced in the absence of an element not disclosed. Furthermore, if there is language referring to order, such as first and second, it should be understood in an exemplary sense and not in a limiting sense. For example, it can be recognized by those skilled in the art that certain steps can be combined into a single step.

The singular forms “a”, “an” and “the” include plural referents, unless the context clearly dictates otherwise.

“Comprising” in a claim is an open transitional term which means the subsequently identified claim elements are a nonexclusive listing (i.e., anything else may be additionally included and remain within the scope of “comprising”). “Comprising” as used herein may be replaced by the more limited transitional terms “consisting essentially of” and “consisting of” unless otherwise indicated herein.

“Providing” in a claim is defined to mean furnishing, supplying, making available, or preparing something. The step may be performed by any actor in the absence of express language in the claim to the contrary.

Optional or optionally means that the subsequently described event or circumstances may or may not occur. The description includes instances where the event or circumstance occurs and instances where it does not occur.

Ranges may be expressed herein as from about one particular value, and/or to about another particular value. When such a range is expressed, it is to be understood that another embodiment is from the one particular value and/or to the other particular value, along with all combinations within said range. 

I claim:
 1. A process for supplying oxygen and/or nitrogen and also argon to a geographic zone comprising n units for air separation by cryogenic distillation, the process comprising the steps of: providing a first unit and n-1 second units; using the first unit to supply argon demands of clients within the geographic zone; using the n-1 second units to produce oxygen and/or nitrogen without producing argon, wherein the oxygen and/or nitrogen for at least certain clients in the geographic zone come from at least one of the n-1 second, non-argon-producing units, and argon for these clients comes from the first unit, wherein the first unit comprises a column system comprising a double column composed of a higher pressure column operating at a first pressure and a lower pressure column, whose bottom is connected thermally to the top of the higher pressure column, operating at a second pressure, which is lower than the first pressure, an argon-producing column, and a mixing column; feeding a bottom of the mixing column with an auxiliary gas comprising gaseous nitrogen that is transferred from the higher pressure column or the lower pressure column, feeding a top of the mixing column with a liquid, which is richer in oxygen than the auxiliary gas, that is transferred from a lower part of the lower pressure column; withdrawing impure oxygen constituting a production gas at the top of the mixing column; feeding the argon-producing column an argon-enriched gas flow from the lower pressure column; and withdrawing an argon-rich product from the argon-producing column.
 2. The process according to claim 1, wherein the argon for these at least certain clients comes solely from the first unit.
 3. The process according to claim 1, wherein at least some of the n-1 second units are halted if the price of electricity increases beyond a threshold.
 4. The process according to claim 3, wherein the first unit is not halted if the price of electricity increases beyond the threshold.
 5. The process according to claim 1, wherein the post-halt steady-state return time for one or even each of the n-1 second units is less than that for the first unit.
 6. The process according to claim 1, wherein the first unit does not supply the clients that it supplies with argon with oxygen.
 7. The process according to claim 1, wherein the first unit supplies all of the clients in a zone with argon and/or constitutes the only unit supplying the clients in the geographic zone with argon.
 8. The process according to claim 1, wherein the first unit receives a flow of air for separation which is greater than that needed to produce a flow of oxygen that it produces as an end product.
 9. Assembly of units for air separation by cryogenic distillation for supplying oxygen and/or nitrogen and also argon to a geographic zone, the assembly comprising: n units for air separation by cryogenic distillation, of which a first unit and n-1 second units produce oxygen and/or nitrogen but do not produce argon; means for transporting the oxygen and/or nitrogen for at least certain clients in the geographic zone from at least one of the n-1 second, non-argon-producing units; and means for transporting argon for these clients from the first unit; wherein the first unit operates by means of a column system comprising: a double column composed of a higher pressure column operating at a first pressure and a lower pressure column, whose bottom is connected thermally to the top of the higher pressure column, operating at a second pressure, which is lower than the first pressure, and of an argon-producing column and a mixing column; means for feeding the mixing column at the bottom with an auxiliary gas consisting of gaseous nitrogen from the first or the lower pressure column, and means for feeding the mixing column at the top with a liquid which is richer in oxygen than the auxiliary gas and is taken from the lower part of the low-pressure column; means for withdrawing impure oxygen constituting a production gas at the top of the mixing column, means for feeding the argon-producing column with an argon-enriched gas flow from the lower pressure column, and means for withdrawing an argon-rich product from the argon-producing column. 